This invention relates to machines for measuring the capacity of cells and, more particularly, relates to a circuit utilized in such machines for discharging a charged cell to a predetermined cell voltage indicative of discharge of the total capacity of the cell.
Electrochemical cells such as nickel cadmium are typically capacity graded as a means of quality control as well as to obtain matched capacity cells for making a battery of series-connected cells.
One prior art apparatus for capacity grading cells is a circuit board in which a plurality of cells are connected in series with a rheostat discharge load. The cells are graded using this apparatus by (1) inserting a plurality of cells in the board, (2) allowing the cells to discharge at constant current while periodically manually checking each of the cells with a voltmeter to measure cell voltage, (3) manually removing cells which have a voltage indicative of substantially total discharge of the capacity of the cell, (4) manually adjusting the rheostat to maintain a constant current discharge for the remaining cells, and (5) sorting the cells based on total discharge time. Such prior art methods require substantial manual labor and are, therefore, costly and unnecessarily complicated.
It is, therefore, an object of this invention to provide a circuit which automatically discharges cells and monitors the cell voltage for use in an automated cell capacity grading machine.